The proposed research deals with a) labelling the transport sites for the tubular secretion of organic anions, b) assessment of the driving force for the tubular transport of organic ions, and c) the effect of toxic chemicals on renal functions. In the first study, NAP-taurine (N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate) will be used to label organic anion transport sites in membrane vesicle preparations. In the second study, attempts will be made to assess the basolateral membrane potential in the rabbit kidney slice by measuring the equilibrium distribution ratio of a lipophilic cation, triphenylmethylphosphonium bromide (TPMP). If this approach proves to be successful, it would greatly facilitate the estimation of electrical driving force across the basolateral membrane for the transport of ions. In the last series, the nephrotoxicity of DDA (bis (p-chlorophenyl) acetic acid), a metabolite of DDT, in the rat will be investigated.